This Week in Cardiology Podcast is Fixed
I did a deep dive into cardiac imaging, focusing on the use of CTA for the diagnosis of coronary artery disease. I think the anatomic imaging test is leading us astray.
This is a post about coronary artery imaging.
But first, in the matter of first world problems, the This Week in Cardiology podcast did not upload properly to the Apple and Spotify platforms yesterday. The Medscape team promptly fixed the issue and the podcast can now be heard in full.
I make note of this because I spent the week studying the use of coronary CT scanning.
Here are a few words about this relatively new way to assess for coronary artery disease. When you present for evaluation of chest pain, we try to diagnose and treat the problem. While chest pain can have many causes, a primary concern is coronary artery disease or CAD.
In days of old there was only “functional” testing for CAD. That is, we stressed the heart, either with exercise or vasodilators, and then assessed for ischemia (demand > supply due to coronary disease).
Inducible ischemia shows up on either the ECG, echo, or nuclear perfusion images. If positive, stress tests provided “indirect” evidence for coronary disease. The doctor could then treat the patient for CAD or refer for invasive coronary angiography—wherein contrast is injected into each of the three coronary arteries.
(Of course, the multimillion dollar ISCHEMIA trial found that there was no difference in outcomes for sending patients with positive stress tests immediately to the cath lab for coronary angiography vs initial medical treatment. But no matter, the train from positive stress tests to the cath lab remains at full capacity in the US.)
Coronary CT scans offer a different way to diagnose CAD. We call these “anatomic” tests—wherein the doctor can see the blockage as contrast goes down the coronary. (Note, a coronary CT is different from a coronary calcium scan. The latter simply measures the amount of calcium in the arteries whereas coronary CT is an actual angiogram of the inside of the vessel.)
The promise of coronary CT is that non-invasive angiography allows a more accurate diagnosis of CAD. Because you can see it.
I was part of a meta-analysis of studies comparing functional and anatomic testing in patients with chest pain.
We found that use of CTA decreased the incidence of MI but increased the use of coronary interventions. CTA vs functional stress testing did not result in a decrease in cardiac hospitalizations or mortality. However, and it was a big however, we were forced by reviewers to include a trial that was dissimilar from all the others.
The question we asked was which method was better to evaluate patients with chest pain—CTA or functional tests. We wanted to include only trials that directly compared the two testing strategies. Those trials, when combined, showed no difference in any outcome.
Peer reviewers, however insisted that we include the SCOT-HEART trial, which found that adding CTA to the normal routine of testing reduced MI in the future. Adding SCOT-HEART drove the positive results (MI) of our meta-analysis.
But there were two issues with SCOT-HEART. One was that it did not directly compare CTA and functional testing. Instead it was a comparison of CTA + functional testing to functional testing alone. So we did not originally include it in our meta-analysis. Peer reviewers insisted, and we had two choices: include it or have the paper rejected.
The second issue with SCOT-HEART arose when the authors presented the five year results, which showed dramatic reductions in MI when adding CTA.
The title of my commentary at that time was: Five Reasons I Don't Believe an Imaging Test Improves Outcomes. See also my post on SCOT-HEART on Sensible Medicine.
I discussed this issue again on this week’s podcast. The short story is that the degree of reduction in MI in SCOT-HEART was outsized and hard to explain.
I went further into CTA imaging on last week’s podcast.
For instance, the test is used in much different ways in the US vs Scotland. In cost-constrained health systems the test is used to decrease the number of expensive angiography and stent procedures. They do this by believing in the evidence and treating any CAD medically. Because that is what the evidence shows.
In the US, it’s the opposite. Hospitals are buying CTA scanners and putting them in ERs and chest pain centers, because the anatomic test finds CAD at higher rates than functional tests. It does not matter that patients can present with totally non-cardiac pain and the CTA finds coincidental CAD.
The culture here is that CAD should be investigated with an invasive angiogram and stented if significant—despite the evidence showing there is no benefit. I call the CTA scanners in the US cash machines because they send more patients to the cath lab than functional tests did.
The other issue I went into on the podcast was a new twist on using CTA called fractional flow reserve or FFR from the CT. This proprietary test from a company called HeartFlow purports to tell doctors whether a partial blockage seen on CTA is tight enough to limit flow. And if it is, that is bad, and it should be fixed.
Of course, FFR is used in the cath lab as well.
My take is that FFR is a flawed measure, no matter where it’s used. I went into detail on one of the seminal studies of CT-FFR, called the ADVANCE registry. I found a darn mess.
Conclusion
Many smart people have advised me not to be critical of a test. A test is just a test. The problem are the humans who misuse the test. That advice fits here. A CTA is a simple picture of coronary arteries. Our job is to use it wisely. That it is misused is the fault of humans not the scanner.
Coronary artery disease is part of the diverse disease of atherosclerosis. CAD treatment therefore should focus on treating atherosclerosis: diet, exercise, good control of blood pressure and cholesterol for instance.
Placing stents in stable partial blockages does not reduce the chance of future MI or death. It’s a hard concept but it’s been borne out by every clinical trial ever done.
If a CTA finds CAD the treatment is not a stent but medical treatment. Then if medical treatment fails, a stent can be considered.
Here are the various places that you can find the podcast. It publishes every Friday afternoon.
This Week in Cardiology podcast on Medscape (with a transcript)
On the one hand, I agree with the contention that the issue is not with the test per se, but with the end users of the results of that test (and the warped financial incentives that serve at cross purposes to proper outcome-driven patient care).
OTOH, it’s a failure of regulators and gate-keepers to authorize /permit/ give credence to a test that has not shown downstream endpoint benefits to begin with. It’s yet another example of regulators failing to properly discharge their fiduciary duties.
THANK YOU John for your always excellent analyses of the cardiac literature. Your critical "eye" for pros, cons & relevance of clinical studies is tremendously appreciated.
QUESTION — What do you perceive as potential role of CTA for the patient who presents to the ED for acute CP (Chest Pain)? I completely agree that incidental finding of preexisting but nonocclusive coronary disease does NOT merit prompt cath with PCI. But is it (or is it not) reasonable in the ED to do CTA looking for clear evidence of a "culprit" artery — which if found, merits cath & PCI? And, if nothing resembling an acute "culprit" iis found — then NOT pursuing prompt cath?
P.S. I ask the above from my perspective of NO LONGER believing in the outdated "STEMI paradigm" — since literature and our recent numerous case examples on Dr. Smith's ECG Blog clearly demonstrate how at least 1/3 of all acute coronary occlusions ( = "OMIs" = Occlusion based MIs) do not satisfy millimeter-based STEMI criteria, yet ARE very often able to be diagnosed by other ECG crieria (ie, hyperacute T waves, more subtle but convincing ST-T wave abnormalities in multiple leads, maximal ST depression in V2,V3 and/or V4 indicating posterior OMI — "dynamic" ST-T abnormalities on repeat ECG, etc.). My bias is that MUCH (most) of the time — awareness and attention to OMI ECG criteria can definitively obviate need for CTA, thereby greatly expediting clear indication for prompt cath.
THANK YOU in advance for your wisdom regarding the above!